Masked Study DesignsStudy designs comparing two or more interventions in which either the investigators, the participants, or some combination thereof do not know the treatment group assignments of individual participants. Sometimes called "blind" study designs. (See also: Double-Masked Design; Single-Masked Design.)

Mature MinorSomeone who has not reached adulthood (as defined by state law) but who may be treated as an adult for certain purposes (e.g., consenting to medical care). Note that a mature minor is not necessarily an emancipated minor. (See also: Emancipated Minor.)

Medical DeviceA diagnostic or therapeutic article that does not achieve any of its principal intended purpose through chemical action within or on the body. Such devices include diagnostic test kits, crutches, electrodes, pacemakers, arterial grafts, intraocular lenses, and orthopedic pins or other orthopedic equipment.

Medical Device Amendments (MDAs)Amendments to the Federal Food, Drug and Cosmetic Act passed in 1976 to regulate the distribution of medical devices and diagnostic products.

Metabolism (of a drug)The manner in which a drug is acted upon (taken up, converted to other substances, and excreted) by various organs of the body.

Minimal RiskA risk is minimal where the probability and magnitude of harm or discomfort anticipated in the proposed research are not greater, in and of themselves, than those ordinarily encountered in daily life or during the performance of routine physical or psychological examinations or tests [Federal Policy §___.102(i)]. For example, the risk of drawing a small amount of blood from a healthy individual for research purposes is no greater than the risk of doing so as part of routine physical examination.

For research involving children, research that does not involve greater than minimal risk requires both assent of the child and permission of at least one parent or guardian.

The definition of minimal risk for research involving prisoners differs somewhat from that given for noninstitutionalized adults. [See 45 CFR 46.303(d) and Guidebook Chapter 6, Section E, "Prisoners."]

Minimal is an adjective, as in "minimal risk"; minimum is a noun, as in "the acceptable minimum."

MonitoringThe collection and analysis of data as the project progresses to assure the appropriateness of the research, its design and subject protections.